Volterra series based predistortion for broadband RF power amplifiers with memory effects

RF power amplifiers(PAs)are usually considered as memoryless devices in most existing predistortion techniques.However,in broadband communication systems,such as WCDMA,the PA memory effects are significant,and memoryless predistortion cannot linearize the PAs effectively.After analyzing the PA memory effects,a novel predistortion method based on the simplified Volterra series is proposed to linearize broadband RF PAs with memory effects.The indirect learning architecture is adopted to design the predistortion scheme and the recursive least squares algorithm with forgetting factor is applied to identify the parameters of the predistorter.Simulation results show that the proposed predistortion method can compensate the nonlinear distortion and memory effects of broadband RF PAs effectively.     

考虑记忆交叉项的宽带功放行为建模方法

针对宽带功率放大器的强记忆效应,提出了一种前馈交叉记忆多项式模型。该模型由主信号对消和畸变注入两个环路构成。信号对消环路采用记忆多项式模型对带内动态线性记忆效应进行建模;畸变注入环路采用记忆时刻信号间的交叉记忆项对带外扩展频谱行为进行建模。为克服最小二乘法在模型辨识中带来的数值不稳定问题,采用共轭梯度的方法对模型的参数进行辨识。为消除噪声和测量误差对模型参数辨识带来的影响,采用ADS软件包络仿真的方法获取精确的功放输入输出信号复包络数据,并对该模型进行充分的性能分析和评估。实验结果表明,所提方法对宽带功放的非线性动态特性具有很好的逼近能力,特别是带外频谱扩展特性,较之常用的方法提升了近10 dB。     

宽带OFDM系统中的简化滤波查表预失真算法

为了解决宽带正交频分复用（orthogonal frequency division multiplexing, OFDM)系统中放大器有记忆非线性特性给系统带来的失真问题,提出了一种简化的滤波查表(simplified filter look up table, S FLUT)预失真方法。该方法由一个无记忆预失真器子系统串联一个自适应滤波器子系统构成,能有效解决放大器带来的失真问题,同时采用简化的自适应更新结构,可以弥补原滤波查表法反馈支路结构复杂、收敛精度低的缺点。     

功放数字基带预失真理论分析和仿真实现

为了消除功放非线性带来的失真,满足制定的功率谱密度要求,自适应数字基带预失真技术以其良好的线性度、宽带宽、高效率和全自适应性等优点而成为消除功放失真的首选.从几种线性化技术的比较开始,介绍了两种数字预失真结构,给出了数字基带预失真的工作原理,构建了数字基带预失真电路并在ADS环境下实现了系统级仿真.仿真结果表明构建的数字基带预失真系统能够获得好的预失真效果,功率谱密度的最大改善能够达到30dBm.创建的系统级仿真电路对实际的数字预失真系统设计起着重要的指导作用.     

宽带正交频分复用系统的记忆型预失真器

提出了一种自适应预失真器及其迭代算法,可同时解决宽带OFDM发射机中功率放大器的非线性和记忆效应问题。该预失真器由均衡器和基于查询表(LUT)的无记忆预失真器串联组成,首先通过窄带训练序列,获得无记忆预失真器的参数,抵消功率放大器的非线性,然后通过迭代算法修改均衡器的参数,补偿功率放大器的记忆效应。与以往解决OFDM功率放大器记忆效应的预失真器相比,迭代算法简单,便于实现。仿真结果表明该预失真器可有效校正和抵消宽带OFDM系统中功率放大器的非线性和记忆效应。     

基于正交模型辨识辅助的欠采样数字预失真方法

针对数字预失真技术在宽带通信系统中的具体实现受到模数转换器采样率制约的问题,提出一种新的欠采样数字预失真方法。首先在欠采样速率下对功放的正交模型进行离线辨识,接着根据一定的算法得到Nyquist采样率下的简化预失真器模型,并进行在线的自适应直接学习。该方法具有预失真器模型构造简单、欠采样实现高效的特点。理论分析和仿真结果表明,该方法有效降低了对模数转换器的采样率要求,优化了简化预失真器模型的线性化条件,更好地抑制了功放非线性引起的带内失真和频谱再生。     

基于阵列接收模型的宽带盲源分离算法

针对传统盲分离算法对宽带信号不适用的问题,提出了一种基于阵列接收模型的宽带盲源分离算法。该算法以子带分解的方法实现了瞬时复值盲分离方法在宽带情形下的扩展。针对扩展过程中可能出现的子带间次序模糊及子带内幅度模糊的问题,利用阵列接收情况下分离矩阵与混合矩阵的特点,提出了一种基于波达方向(direction of arrival, DOA)估计的次序调整及幅度去模糊方法。仿真结果表明,该算法不仅能有效地分离宽带信号,而且可准确地恢复出信号幅度。     

A simplified decoding algorithm for multi-CRC polar codes

Polar codes represent one of the major breakthroughs in 5G standard,and have been proven to be able to achieve the symmetric capacity of binary-input discrete memoryless channels using the successive cancellation list(SCL)decoding algorithm.However,the SCL algorithm suffers from a large amount of memory overhead.This paper proposes an adaptive simplified decoding algorithm for multiple cyclic redundancy check(CRC)polar codes.Simulation results show that the proposed method can reduce the decoding complexity and memory space.It can also acquire the performance gain in the low signal to noise ratio region.     

Finding Efficient Solutions for Multiobjective Decision Making

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基于HPA特性曲线拟合的自适应预失真技术

提出了一种用于正交频分复用(OFDM)系统中补偿由大功率放大器引起的非线性失真的基带自适应预失真方法。自适应预失真器是基于对大功率放大器的非线性特性进行分段估计,由曲线拟合逐段取逆变换来训练大功率放大器的预失真器的非线性参数,以达到预是真补偿的目的。计算机仿真结果表明,该方法具有收敛速度快、需要动态存储器(RAM)少、补偿效果好等特点。     

基于阵列信号处理的新型虚拟暗室测试方法

在复杂电磁环境中,如何对电子设备产生的电磁辐射进行准确测量一直是亟待解决的典型工程问题。提出了一种具有环境干扰抑制效果的外场辐射发射测试新方法,不同于传统的基于自适应噪声抵消方式的虚拟暗室测试方法,其采用空间谱估计和自适应宽带波束形成等阵列信号处理方式以实现对环境干扰的空域滤除。计算机仿真以及试验结果证明,所提方法在保证受试设备辐射特性无失真的情况下,能同时有效滤除被测信号中混迭的同频、宽带等不同体制的环境干扰,弥补了虚拟暗室测试技术的不足,提高了外场电磁辐射测量的速度和精度。     

宽带相控阵雷达中波束形成问题的研究

多功能宽带相控阵雷达可以灵活地切换于多种工作模式和实现高分辨成像,成为相控阵雷达发展的重要方向。工作在成像模式时,系统采用具有一定带宽的信号,传统窄带波束形成的方法在宽带相控阵雷达中不再适用。对宽带相控阵雷达中波束形成问题进行了讨论,对波束方向图的畸变给出了定量分析和实验结果。在此基础上,提出了频域宽带波束形成方法中频率柜划分的依据。     

基于极化状态配置的宽带相控阵极化控制方法

传统的固定极化状态存在交叉极化隔离度低且有效的扫描角度范围窄等问题,制约了相控阵雷达中极化信息的充分利用.为提高交叉极化隔离度,并解决宽带相控阵中波束方向图畸变问题,提出一种基于极化状态配置方法的宽带相控阵极化方向图综合方案.通过优化不同波束指向的极化状态,并利用有限长单位冲激响应(finite impulse res...     

基于特征向量空间聚焦的宽带DOA估计方法

针对传统宽带阵列信号波达方向(direction of arrival,DOA)估计方法中由入射角预估带来的DOA估计偏差及其在多径效应等环境下的应用问题,提出基于特征向量空间聚焦的宽带阵列DOA估计方法.首先,考虑多径干扰等对DOA估计算法的影响,对接收信号自相关矩阵进行平滑处理.然后,以平滑自相关矩阵特征向量空间过...     

GNSS接收机射频前端电路相位噪声评估方法

相位噪声是影响全球卫星导航系统(global navigation satellite system, GNSS)接收机性能的一个重要因素,在高性能的接收机设计中,射频前端电路的相位噪声评测是不可忽略的。传统观测相位噪声的方法主要是利用频谱分析仪等专业仪器来实现,其无法观测GNSS接收机射频前端电路(包含模数(analog-digital,AD)转换器)的相位噪声。分析了接收机相位噪声和热噪声在信号复平面域的表现特征,提出了在信号复平面域评估GNSS接收机射频前端电路相位噪声的方法,并对该方法进行了仿真验证和实测验证。利用相位噪声对信号在复平面实部和虚部影响不同的特点,对采集到的信号数字中频数据进行相干积分处理,定量估算接收机射频系统的相位噪声。结果表明,该方法具有较高的评估准确度,可以用于测量与评估GNSS接收机射频前端电路(包含AD转换器)的设计质量,预测接收机性能。     

Delay-independent robust guaranteed-cost control for uncertain linear neutral systems

This article concerns the delay-independent guaranteed-cost control problem via memoryless state feedback for a class of neutral-type systems with structural uncertainty and a given quadratic cost function. New delay-independent conditions for the existence of the guaranteed-cost controller are presented in the term of LMIs. An algorithm involving optimization is proposed to design a controller achieving an optimal guaranteed-cost, such that, the system can be stabilized for all admissible uncertainties. A numerical example is provided to illustrate the feasibility of the proposed method.     

线性插值基的数字预失真方法

随着射频功率放大器的发射功率不断提升,特别是Doherty功放的广泛应用,使得功放的非线性特性不断增强。为了满足高线性化的需求,数字预失真(digital pre distortion, DPD)技术要求达到更优的非线性校正效果。提出一种基于线性插值基的数字预失真方法,所提方法将线性插值基引入到数字预失真的行为建模中,达到优化的非线性校正效果。同时所提方法通过与查找表的实现方式结合,非常利于系统应用。仿真实验中采用20 MHz长期演进(long term evolution, LTE)信号进行实验,新方法较广义记忆多项式方法在临道泄露比指标上改善了近7 dBc以上。     

Novel reference range selection method in InlSAR imaging

Aiming at the reference range selection for different antennas in interferometric inverse synthetic aperture radar (InISAR) systems, this paper proposes a respective focusing (RF) method. The reference ranges for echoes of different antennas are selected respectively for RF, which is different from the traditional uniform focusing (UF) with the same reference range applied to all the antennas. First, a comparison between UF and RF for InISAR signal model considering the ranging error is given. Compared with RF, UF has an advantage in overcoming the ranging error differences between different antennas. Then the influence of ranging error upon the interferometric imaging with RF is investigated particularly, and it is found that the ranging error differences between different antennas are far smaller than the wavelength, which is advantageous to imaging. By comparing the capabilities of interferometric imaging between RF and UF, it is concluded that RF is a better choice in conquering problems such as image mismatching and phase ambiguity even with ranging errors. Simulations demonstrate the validity of the proposed method.     

Robust stability and stabilization for uncertain discrete-time switched singular systems with time-varying delays

The problems of robust stability and stabilization via memoryless state feedback for a class of discrete-time switched singular systems with time-varying delays and linear fractional uncertainties are investigated. By constructing a novel switched Lyapunov–Krasovskii functional, a delay-dependent criterion for the unforced system to be regular, causal and uniformly asymptotically stable is established in terms of linear matrix inequalities (LMIs). An explicit expression for the desired memoryless state feedback stabilization controller is also given. The merits of the proposed criteria lie in their less conservativeness and relative simplicity, which are achieved by considering additionally useful terms (ignored in previous methods) when estimating the upper bound of the forward difference of the Lyapunov–Krasovskii functional and by avoiding utilizing any model augmentation transformation. Some numerical examples are provided to illustrate the validity of the proposed methods.     

线性时滞系统的记忆与无记忆复合$H^{\infty}$状态反馈控制

对于存在状态时滞的线性时滞系统 ,研究了无记忆与带记忆的复合 $H^{\infty}$ 状态反馈控制器的设计问题 ,通过解相应的线性矩阵不等式求得满足设计要求的状态反馈控制器 ,得到了很好的控制效果 .最后给出一个数字仿真实例说明所得结论的有效性 .